EXAMINATION OF SPECIES BOUNDARIES OF SOLANUM SERIES DEMISSA AND POTENTIALLY RELATED SPECIES IN SERIES ACAULIA AND SERIES TUBEROSA (SECT PETOTA)

Species boundaries were assessed by phenetic analyses of morphological data for Solanum sect. Petota series Demissa: S. brachycarpum, S. demissum, S. guerreroense, S. hougasii, S. iopetalum, and S. schenckii. These six hexaploid (2n = 6x = 72) wild potato species grow in Mexico and Guatemala and constitute all the tara of series Demissa except three pentaploid hybrids involving crosses with species from other series. We also analyzed two species, S. albicans (series Acaulia) and S. verrucosum (series Tuberosa), that are morphologically very similar to some members of series Demissa. We chose these species because S. verrucosum has been hypothesized to be a progenitor in the hybrid origin of all species in series Demissa, and because S. albicans is very similar to S. demissum. The results show that S. albicans, S. brachycarpum, S. demissum, S. schenckii, and S. verrucosum are supported by multivariate analyses, but are inconclusive regarding species boundaries of the rare taxa S. hougasii, S. guerreroense, and S. iopetalum, and more collections are needed to resolve their taxonomic status. Extensive overlap of species-specific character states shows the difficulty of the preparation of keys, diagnosis of taxa, and cladistic analyses in this group. The results also show that S. demissum is phenetically more similar to S. albicans than to other species in series Demissa and that S. verrucosum is similar to S. schenckii, and they question the assignment of these species into series.